Waveguide fed frequency independent antenna



April 28, 1970 N. BARBANO 3,509,572

WAVEGUIDE FED FREQUENCY INDEPENDENT ANTENNA 5 Sheets-Sheet 1 Filed Dec. 8, 1966 INVENTOR.

NORMAND BARBANO ATTORNEY April 28, 1970 N. BARBANO 3,509,572

WAVEGUIDE FED FREQUENCY INDEPENDENT ANTENNA Filed Dec. 8, 1966 5 Sheets-Sheet 2 INVENTOR.

NORMAN D BAR BANO ewrj fad/k ATTOR NEY April 28, 1970 N. BARBANO 3,509,572

WAVEGUIDE FED FREQUENCY INDEPENDENT ANTENNA Filed Dec. 8, 1966 5 Sheets-Sheet 5 INVENTOR. NORMAND BARBANO ATTOR NEY N. BARBANO 3,509,572

WAVEGUIDE FED FREQUENCY INDEPENDENT ANTENNA April 28, 1970 5 Sheets-Sheet 4 Filed Dec. 8, 1966 Ln INCHES mmwmwmo maI FREQUENCY -GC/S 1 5 INVENTOR.

NORMAND BARBANO M BY ATTORNEY April 28, 1970 N. BARBAN'o WAVEGUIDE FED FREQUENCY INDEPENDENT ANTENNA Filed Dec. 8, 1966 5 Sheets-Sheet 5 E 1 El mummomo 3mm.

FREQUENCY- 60/8 I INVENTOR.

I NORMAND BARBANO m, )4za/& BY

ATTORNEY United States Patent 3,509,572 WAVEGUIDE FED FREQUENCY INDEPENDENT ANTENNA Normand Barbano, Sunnyvale, Calif., assignor t0 Sylvania Electric Products Inc., a corporation of Delaware Filed Dec. 8, 1966, Ser. No. 600,144 Int. Cl. H01q 11/10 US. Cl. 343-7925 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to antennas exhibiting pseudofrequency independent operation and more particularly to an improved log periodic antenna which is fed by a waveguide,

Log periodic antennas have the desirable characteristic of maintaining a relatively constant radiation pattern and impedance over indefinitely large bandwidths. Most log periodic antennas include some form of tapered-V or parallel-two-wire transmission line feeder system such as are described and referenced in IRE International Convention Record, part I, 1961, pages 76-85. A log periodic dipole antenna which incorporates an improved and simplified feed system and is electrically symmetrical about the longitudinal axis of the antenna is disclosed in my Patent No. 3,286,268, Log Periodic Antenna With parasitic Elements Interspersed in Log Periodic Manner, assigned to the assignee of this invention. Printed circuit antennas in accordance with my invention in the above patent may be constructed wherein the parasitic elements are etched in copperclad on one side of a printed circuit board and the driven element and a two-wire transmission line feed are etched in the copperclad on the other side of the printed circuit board.

At high frequencies, e.g., in the SHF band, it is difficult to provide a satisfactory feed for log periodic antennas. The two-wire transmission line feeder system becomes more impractical as frequency increases because the size of the conductors of the two-wire line varies inversely with frequency. This relationship is required to maintain a reasonable element rank to feeder line (conductor) size and thus maintain the antenna patterns relatively constant over the band. This decrease in the size of the conductors of the two-wire line causes an increase in losses in the feed line and a resultant decrease in the gain and efficiency of the antenna. Also, as the size of the feed line conductors decrease, tolerances on elements of the feed line must become tighter causing a resultant increase in the cost of manufacture of the antenna. The efiiciency of the printed circuit log periodic antenna also decreases at higher frequencies because of increasing dielectric losses.

An object of this invention is the provision of an improved frequency independent antenna for operation at high frequencies.

SUMMARY In accordance with this invention, the system for feeding a log periodic antenna comprises a waveguide transmission line. A log periodic dipole antenna incorporating this invention comprises a plurality of parallel pairs of conductive elements. The elements of each pair are located 3,509,572 Patented Apr. 28, 1970 on opposite sides of a Waveguide feed and are normal to, electrically insulated from, and extend through an associated narrow wall of the waveguide. The lengths of and spacings between the portions of the conductive elements outside the waveguide increase logarithmically from one end of the antenna to the other. The end of each element inside the waveguide comprises a probe or length of conductor parallel to and coupled to the electric field in the waveguide, The probes on each dipole set, as well as the probes on axially adjacent elements, extend in opposite directions so that currents induced in the elements outside the waveguide are out-of-phase as is required for pseudo-frequency-independent operation. In a modified form of this invention, the elements of axially alternate dipoles do not extend into the waveguide but are directly electrically connected to the associated narrow walls of the Waveguide. The probes on the remaining dipole elements which are insulated from the waveguide, extend in the same direction. In another form of the invention, the elements of axially alternate dipoles are electrically insulated from and extend perpendicularly through an associated broad wall of the waveguide. The portions of the elements of these alternate dipoles inside the waveguide are parallel to the electric field. The elements of the other dipoles do not extend into the waveguide but are electrically connected to the associated broad wall of the waveguide. It has been discovered that the pseudo-frequency-independent operation of these waveguide feed log periodic antennas is improved by varying the length and spacing of the conductive elements slightly from the geometric ratio 'r in order to compensate for the dispersive effects caused by the conductive sheath comprising the waveguide and the probes in the waveguide.

DESCRIPTION OF DRAWINGS This invention Will be more fully understood from the following detailed description of preferred embodiments thereof, together with the accompanying drawings where- FIGURE 1 is a perspective view of a Waveguide fed log periodic dipole antenna embodying this invention;

FIGURE 2 is similar to a transverse section of FIG- URE 1 but shows only one dipole element and the electric field pattern in the waveguide;

FIGURE 3 is a perspective view of a portion of the Waveguide of FIGURE 1;

FIGURE 4 is a curve of a corr ction factor for determining the length of the probe in the waveguide;

FIGURE 5 is a perspective view of a waveguide fed log periodic Yagi-Uda dipole antenna embodying this invention;

FIGURES 6-10 are transverse sections of waveguide antennas showing different orientations of the probe of an element of a log periodic antenna in different types of waveguide feed, wherein FIGURE 6 is similar to a transverse section of FIG- URE 5 but shows only one dipole element and the electric field pattern in the waveguide,

FIGURE 7 shows elements extending through both the broad and narrow walls of a ridged waveguide and coupled to the electric field between the ridges,

FIGURE 8 shows elements extending through the wall of and coupled to the electric field supported by a circular waveguide, and

FIGURES 9 and 10 show elements coupled through the broad and narrow walls, respectively, of a rectangular waveguide and coupled to the magnetic field in the waveguide;

FIGURE 11 is a perspective view of a Waveguide fed log periodic Yagi-Uda monopole antenna embodying this invention;

FIGURE 12 is H-plane antenna patterns illustrating the operation of a waveguide fed log periodic monopole antenna similar to the antenna of FIGURE 1 which was built and tested;

FIGURE 13 is a plan view of a modified form of this invention wherein the ratio of element lengths is varied from the geometric ratio 1- for providing improved pseudo-frequency-independent operation;

FIGURE 14 depicts curves showing the relationships of element lengths and spacings of the antenna of FIG- URE 13 and conventional waveguide fed log periodic monopole antennas;

FIGURE 15 shows curves illustrating the comparative operation of the antenna of FIGURE 13 and conventional waveguide fed log periodic monopole antennas;

FIGURE 16 is a plan view of a modified form of this invention wherein the ratio of element lengths is varied from the geometric ratio T;

FIGURE 17 depicts curves showing the relationships of element lengths and spacings of the antenna of FIG- URE 16 and a conventional waveguide fed log periodic antenna; and

FIGURE 18 shows curves illustrating the comparative operation of the antenna of FIGURE 16 and a conventional waveguide fed log periodic monopole antenna.

DESCRIPTIONS OF PREFERRED EMBODIMENTS The antenna of FIGURE 1 comprises a rectangular waveguide transmission line feed 1 and pairs of conductive elements 3 and 3' to 7 and 7, inclusive, which function as dipoles. The ends of the waveguide are closed by shorting plates 9 and 10. A waveguide to coax adapter 11 in broad wall 12 adjacent to plate 9 couples electromagnetic wave signals to and from the waveguide. The waveguide is terminated with a resistive load 13 comprising a dielectric wedge coated with a lossy material such as powdered carbon. The load 13 is connected to plate 10 and centered in the waveguide.

Elements 3-7 and 3-7' are parallel to each other and perpendicular to opposed narrow waveguide walls 16 and 17, respectively, through which the elements extend. Each element is oriented and supported in the waveguide similar to the single representative element 3 in FIGURE 2. Element 3 comprises a radiating section 3a outside the waveguide and a probe section 3b and connecting section 30 inside the waveguide. Element 3 is electrically insulated from and supported on waveguide wall 16 by a spacer 18 of electrically nonconductive material such as Teflon.

It is understood that the antenna can be used to both radiate and receive electromagnetic wave signals. The term radiating section used herein is intended to include the sections, such as the section 3a, of the element outside the waveguide used for receiving as well as radiating electromagnetic wave signals.

The electric field pattern of the dominant TE mode in rectangular waveguide is represented by curved line 19 in FIGURE 2 which approximates the amplitude and distribution of field vectors indicated as arrows 20. Probe 3b preferably is centered in the waveguide between narrow walls 16 and 17 and extends parallel to the electric field vectors for producing a maximum signal current transfer between probe section 3b and the waveguide. The direction of the current in radiating section 3a corresponding to the electric field shown and is represented by arrow 21. A current is not induced in connecting section 3c because it is perpendicular to the electric field in the waveguide.

In order to obtain pseudo-frequency-independent operation from a log periodic dipole antenna, the currents in adjacent and opposite radiating sections (e.g., sections 312, 4a and 3a, 3a, respectively) must be excited 180 out-of-phase. This phase reversal is accomplished in accordance with this invention by pointing the probes (e.g., probes 3b and 4b, 3b and 3b, respectively) of adjacent and opposite elements in opposite directions. This is clearly illustrated in FIGURE 3 wherein probes 3b and 4b extend toward the opposite broad walls 22 and 12, resepctively, and probes 3b and 3b also extend in opposite directions toward the broad walls 22 and 12, respectively. The direction of the currents induced in the respective probes 3b, 3b, and 4b, 4b are indicated by the arrows 23, 24, and 25, 26, respectively. Arrows 23 and 24 indicate that the currents induced in probes 3b and 3b are in-phase. Arrows 29 and 30, however, indicate that the currents produced in the associated radiating sections 3a and 3a are out-of-phase as is required for pseudo-frequencyindependent operation. Similarly, arrows 29 and 31 indicate that currents produced in adjacent radiating elements 3a and 4a are 180 out-of-phase. Thus, this orientation of the probes in the waveguide provides the proper phase relationship of currents produced in the radiating sections for pseudo-frequency-independent operation.

The outer ends of the element radiating sections on both sides of the waveguide are on lines which intersect at a point X (not shown) to the right of elements 7 and 7, as viewed in FIGURE 1. The lengths of and spacings between adjacent radiating elements increase from right to left as viewed and are related by the constant scale factors where VTis a constant having a value less than one, I is the length of the nth radiating section from point X, [(M1) is the length of the adjacent longer section x is the distance from point X to the radiating section I x n+1 is the corresponding distance to the radiating section l and s is the spacing between the radiating section I and the adjacent shorter radiating section.

This antenna radiates in the backfire direction, to the right as viewed in FIGURE 1. Conductive ground planes or plates 33 are connected to the waveguide flush with the narrow walls of the waveguide to reduce the effects of the waveguide structure or antenna operation.

In order to maintain the VSWR and gain of the antenna substantially constant, it is desirable to decrease the length of the probes from their maximum obtainable length. The curve of FIGURE 4 was derived from experimental data and is a plot of the length L of the probe (e.g., probe 3b) as a function of the length H of the radiating section (e.g., radiating section 3a), both lengths L and H being normalized to the inside height b of the narrow wall of the waveguide.

A modified form of this invention having increased directivity is shown in FIGURE 5. The pairs of raidating sections 35 and 35' to 42 and 42', inclusive, are associated with the broad walls 43 and 44 of waveguide 45. The lengths and spacings of the radiating sections 35a, etc., are determined as described in relation to the embodiment of FIGURE 1. The even-numbered or longitudinally alternate elements are oriented and supported in the waveguide similar to the element 36 in FIGURE 6. The element 36 comprises a radiating section 36a outside the waveguide and a probe section 36b in the waveguide parallel to the electric field represented by arrows 46. Elements 36 are supported in and insulated from the waveguide by spacers 18. The lengths of the probes are determined by the relationship shown in FIGURE 4.

The odd-numbered alternate elements comprise radiating sections that are directly electrically connected to the associated broad walls of the waveguide as in FIGURE 5 and do not extend inside the waveguide. The requisite phase relationship of currents in adjacent elements is established by mutual coupling between driven radiating sections (even-numbered elements) and adjacent parasitic radiating secions (odd-numbered elements) as described in my Patent No. 3,286,268.

FIGURE 7 shows elements 48 and 49 located in the broad and narrow walls, respectively, of a double-ridged rectangular waveguide 50 for coupling to the electric field induced therein. Similarly, FIGURE 8 shows elements 52 and 53 in the wall of a circular waveguide 54 for coupling to the electric field supported therein.

FIGURE 9 shows an element 56 in the broad wall of a rectangular waveguide 57 having a probe section 56b comprising a coupling loop for coupling to the magnetic field in the waveguide. The embodiment of FIGURE is similar to that of FIGURE 9 except that the element 58 is located in the narrow wall of waveguide 59.

All of the radiating sections of the elements in the preferred embodiments of this invention in FIGURES 1 and 5 are parallel and aligned in the same plane. It has been found, however, that the axially aligned elements (e.g., the elements 3 to 7 and 3' to 7', see FIGURE 1) associated with opposite walls (e.g., walls 16 and 17, respectively, see FIGURE 1) of the waveguide may be located in planes which are spaced apart. For example, the elements 3 to 7 may be aligned in a plane closer to wall 12 than wall 22 whereas the elements 3 to 7' are axially aligned in a plane that is closer to wall 22 than wall 12. It has also been found that the axially aligned alternate elements (e.g., the odd-numbered elements 35 to 41 and the even-numbered elements 36 to 42, see FIG-. URE 5) in the same waveguide wall (e.g., the associated wall 43 in FIGURE 5) may be located in the planes which are spaced apart. It was determined empirically that these planes containing the elements may be spaced apart approximately one-quarter of the of the height of the shortest radiating section without a significant change in operation.

The dipole antennas of FIGURES 1 and 5 are essentially a pair of log periodic monopole antennas arranged back-to-back in opposite walls of the waveguide. The dipole antenna can be converted to a monopole antenna by removing from the waveguide the elements associated with one of the waveguide walls. No special connections are required to feed the remaining elements of the antenna to provide pseudo-froquency-independent operation.

The antenna shown in FIGURE 11 is a waveguide fed Yagi-Uda monopole antenna in which the elements 61 to 65, inclusive, are located in the narrow wall 66 of Waveguide 67. The alternate elements 62 and 64 are directly electrically connected to wall 66. The other elements 61, 63, and 65 are insulated from wall 66 and comprise probe sections 61b, 63b, and 65b, respectively, aligned in the same direction within the waveguide. An electromagnetic wave signal is coupled directly to waveguide 67 through a second waveguide 68. 3 By way of example, a waveguide" fed log periodic monopole antenna array of the type shown in FIGURE 1 and having the following dimensions and operating characteristics was built and successfully tested.

Number of elements-11 Length of longest element-l.3000 inches Length of shortest element0.587 inch Element diameter--0.125 inch Spacer:

Maximum diameter0.l875 inch Minimum diameter0.125 inch Height extending into waveguide-flush Height above waveguide0 .050* inch 6 Waveguide:

Width (inside)2.840 inches, Height (inside)1.340 inches Wall thickness-41080 inch Frequency range2.603.95 gI-Iz.

The operation of this antenna is shown in part in the H-plane antenna patterns of FIGURE 12. The operating bandwidth is limited to the waveguide bandwidth. These patterns are taken in a plane orthogonal to the E-plane and inclined 25 to the ground plane. These patterns show a well-formed beam of about 78 half-power beamwidth in the H-plane. This corresponds to about 11 db directive gain above that of an isotropic radiator. Gain and E-plane pattern shape are relatively constant over the entire frequency range. The beam shape in the H-plane, however, does change slightly.

The patterns shown in FIGURE 12 indicate that the H-plane antenna pattern, or more specifically the halfpower beamwidth, varies approximately 28 percent over a 52 percent bandwidth. The half-power beamwidth of a conventional log periodic antenna fed by a two-wire transmission line, such as the antenna described in Patent No. 3,286,268, varies approximately 10 percent over a similar bandwidth. The variations of the antenna patterns of FIGURE 12 are believed to be caused by the dispersive effects of the coupling probes and the waveguide on the phase velocity of electromagnetic waves in the waveguide. Since the phase velocity of the electromagnetic waves in a waveguide is a nonlinear function of frequency, the relative phase of currents induced in the probes vary as a function of frequency. The presence of the coupling probes in the waveguide also causes the phase velocity of electromagnetic waves in the waveguide and adjacent the coupling probes to decrease. The resultant effect of the presence of the coupling probes in the waveguide is to cause the phase velocity of the electromagnetic wave to also be a nonlinear function of frequency. The phase velocity has been determined empirically to be a function of probe spacings, probe lengths, and probe diameters.

A modified form of this invention wherein the ratio of spacings between elements is Varied from the geometric ratio 1- to compensate for the nonlinear effects of the phase velocity of signals in the waveguide feed is illustrated in FIGURE 13. This monopole antenna is similar to the dipole antenna of FIGURE 1 and comprises a plurality of elements 71-78, inclusive, perpendicular to the narrow walls of waveguide 79. An electromagnetic wave signal is applied to the waveguide through waveguide-tocoax adapter 80. The ratio of the lengths of the radiating sections satisfy the scale factor /=0.895. The spacings between elements, however, were determined empirically to provide improved pseudo-ferquency-independent operation. The lengths of and spacings between radiating sections of an antenna that was actually built and tested, and whose operation is shown in FIGURE 15, are listed in Table 1.

TABLE 1 Length 1 (inch) Spacing 8 (inch) The spacing s in Table 1 is the distance between the referenced element and the adjacent shorter element. A line AA is drawn between the tips of elements 71 and 78 to show that their respective lengths deviate from the linearly progressive change typical of other log periodic antennas.

The curves of FIGURE 14 are plots of element spacings as a function of the length of radiating sections of the antenna of FIGURE 13 (Table 1) and so-called conventional Waveguide fed log periodic antennas. The term conventional means that the ratios of the spacigs and lengths of the radiating sections both satisfy the geometric ratio 7'. Curves 83 and 84 correspond to an antenna similar to the one shown in FIGURE 13 wherein the ratios of both the lengths and spacings of radiating sections satisfy the geometric ratio 7-, and wherein the included angle is 20 and 30, respectively. Curve 85 corresponds to the antenna of FIGURE 13 wherein the element spacings vary as shown in Table l. The geometric ratio 1- is 0.80 for all of these antennas.

The curves of FIGURE 15 are plots of the half-power beamwidth as a function of frequency which illustrate pseudo-frequency-independent operation of the antenna of FIGURE 13 (Table 1) and conventional waveguide fed log periodic antennas. Curves 86 and 87 show the operation of conventional waveguide fed log periodic antennas corresponding to the curves 83 and 84, respectively. Curve 88 shows the operation of the antenna of FIGURE 13 corresponding to the curve 85. These curves indicate that the half-power beamwidth of the antenna of FIGURE 13 varies less than 6 (8 percent) over a frequency band of 52 percent whereas the half-power beamwidth of the conventional antennas described by curves 83 and 84 varies more than 24 (31 percent) over the same frequency band.

Another modified form of this invention wherein the ratio of the lengths of adjacent radiating sections is varied from the geometric ratio 1- for providing improved pseudo-frequency-independent operation is illustrated in FIGURE 16. This monopole antenna is similar to the dipole antenna of FIGURE 1 and comprises a plurality of elements 91 to 102, inclusive, perpendicular to the narrow walls of waveguide 103. An electromagnetic signal is applied to the waveguide through waveguide-tocoax adapter 104. The ratio of element spacings satisfies the scale factor V'1=O.922. The lengths of the radiating sections were determined empirically, however, to provide improved pseudo-frequency-independent operation. The lengths and spacings of radiating sections of an antenna that was actually built and tested, and whose operation is shown in FIGURE 18, are listed in Table 2.

TABLE 2 Element Length l (inch) Spacing 8 (inch) The curves of FIGURE 17 are plots of element spac ings as a function of lengths of radiating sections of the antenna of FIGURE 16 (Table 2) and a conventional waveguide fed log periodic antenna. Curve 106 corresponds to an antenna similar to that in FIGURE 16 wherein the ratios of lengths and spacings of radiating sections both satisfy the geometric ratio 7:0.85 and wherein the included angle is 20. Curve 107 corresponds to the antenna of FIGURE 16- wherein the length of radiating sections vary as shown in Table 2. The ratio of spacings of elements satisfies the geometric ratio 1:0.85.

The curves of FIGURE 18 are plots of half-power beamwidth as a function of frequency which illustrate pseudo-frequency-independent operation of the antenna of FIGURE 16 (Table 2) and a conventional waveguide fed log periodic antenna. Curve 108 shows the operation of the conventional waveguide fed g periodic antenna described by curve 106. Curve 109 shows the operation of the antenna of FIGURE 16 described by curve 107. Reference to these curves reveals that the half-power beamwidth of the antenna of FIGURE 16 varies less than 10 (15 percent) over a frequency band of 52 percent whereas the half-power beamwidth of the conventional antenna described by curve 106 varies more than 24 (37 percent) over the same band of frequencies.

Although this invention has been described in relation to specific embodiments thereof, variations and modifications will be apparent to those skilled in the art. For example, both the element lengths and element spacings may be varied so as to depart from the geometric ratio 1- in order to provide improved pseudo-frequency-independent operation. Thus, the scope and breadth of the invention is, therefore, to be determined from the following claims rather than from the above detailed description.

What is claimed is:

1. A log periodic antenna having pseudo-frequencyindependent operation and a longitudinal axis, comprising:

a waveguide for propagating electromagnetic wave signals and supporting electric and magnetic fields associated therewith, said waveguide having a longitudinal axis parallel to the axis of the antenna,

a plurality of axially and differentially spaced conductive elements associated with said waveguide, each of said elements comprising:

a first section outside of said waveguide, and a second section inside said waveguide,

means for electrically insulating said elements from said waveguide, and

means for coupling said elements to at least one of said fields in said waveguide so that electric currents in axially adjacent element are out-ofphase with each other, said coupling means comprising:

portions of said second sections extending parallel to the electric field in the waveguide,

said elements being oriented such that said parallel portions of the second sections of adjacent elements extend in opposite directions.

2. The antenna according to claim 1 wherein:

said waveguide has a rectangular cross-section and two pairs of opposite walls,

said insulating means being located in one wall of one of said pair of walls,

each of said elements having a third section disposed within said waveguide and extending perpendicular to the planes of the other pair of walls and parallel to the electric field in the waveguide,

said coupling means comprising said third sections of said elements,

said elements being oriented so that the third sections of adjacent elements extend in opposite directions.

3. The antenna according to claim 2 having a ground plane electrically connected to one wall of said one pair of walls, dimensions and axial spacings of said first sections of adjacent elements increasing in the direction of the axis of the antenna.

4. The antenna according to claim 3 wherein the lengths of said third sections of the elements vary from the minimum to the maximum length element according to the relationship y=0.45, x 0.6 where x=H/ b, H is the length of said first section, b is the minimum spacing between opposite waveguide walls, y=L/b, and L is the length of said third section.

5. A log periodic antenna having pseudo-frequencyindependent operation and a longitudinal axis comprismg:

a waveguide for propagating electromagnetic wave signals and supporting electric and magnetic fields associated therewith, said waveguide having a longi tudinal axis parallel to the axis of the antenna,

a plurality of axially and differentially spaced conductive elements associated with said waveguide, axially alternate elements being electrically connected to said waveguide, the remaining elements each comprising:

a first section outside of said waveguide, and a second section within said waveguide,

means electrically insulating said remaining elements from said waveguide, and

means for coupling said remaining elements to at least one of said fields in said waveguide so that electric currents in said remaining elements are in-phase with each other, mutual coupling between said alternate and remaining elements inducing currents in said alternate elements, said currents in axially adjacent elements being 180 out-of-phase with each other.

6. The antenna according to claim wherein said coupling means comprises:

portions of said second sections perpendicular to the waveguide axis and parallel to each other and to the electric field in the waveguide.

7. The antenna according to claim 5 wherein:

said waveguide has a rectangular cross-section and two pairs of opposite walls,

said insulating means being located in one wall of one of said pairs of walls,

said axially alternate elements being connected to said one wall,

each of said remaining elements including a third section in said waveguide perpendicular to the planes of the other pair of walls and parallel to each other and the electric fields in the waveguide,

all of said third sections of said remaining elements extending in the same direction.

8. The antenna according to claim 5 including:

a ground plane electrically connected to and coextensive with said one wall of said one pair of walls, the lengths and axial spacings of the sections of axially adjacent elements outside the waveguide are related by the log periodic design characteristics of geometric ratio T, where 1- is a number less than one.

'9. The antenna according to claim 5 including:

first and second electrically conducting plates connected to said waveguide walls at the ends thereof and closing the ends of said waveguide,

a termination located in one end of said waveguide,

and

a waveguide-to-coaxial transmission line adapter in a waveguide wall perpendicular to the electric field in pendent operation and a longitudinal axis, comprising:

a waveguide for propagating electromagnetic wave signals and supporting electric and magnetic fields associated therewith, said waveguide having two pairs of opposite walls and a longitudinal axis parallel to the axis of the antenna,

a first plurality of axially spaced conductive elements associated with one wall of one of said pairs of waveguide walls,

a second plurality of conductive elements associated with the other wall of said one pair of walls,

means for coupling said elements to at least one of said fields in said waveguide so that electric currents in axially adjacent elements are out-of-phase with each other,

means for electrically insulating said elements from said Waveguide,

said elements each comprising:

a first section located outside said waveguide,

a second section within said Waveguide, and

a third section within said waveguide extending perpendicular to the planes of the other pair of walls and parallel to the electric field in said waveguide,

the first sections of all of said elements being parallel and in the same plane perpendicular to the planes of said first pair of walls,

the first section of each element being aligned with the first section of a corresponding element on the opposite side of said Waveguide,

the third sections of each pair of opposed elements extending oppositely.

References Cited UNITED STATES PATENTS 2,496,242 1/1950 Bradley 343-814 2,597,144 5/1952 Clapp- 343771 3,007,168 10/1961 Kuecken 343-854 3,127,612 3/1964 Granger 343-7925 ELI LIEBERMAN, Primary Examiner US. Cl. X.R. 

